The invention disclosed and claimed herein pertains to apparatus for scanning graphic information contained upon light transmissive plates, such as microimages, to provide electrical signals which represent or encode the information. More particularly, the invention pertains to apparatus for parallel scanning, or for simultaneously scanning all of the microimages included in a row of a matrix of microimage spaces. Even more particularly, the invention pertains to scanning apparatus of the above type which is provided with means for sensing that a given space of the matrix is not occupied by a microimage.
It is presently well known to store the graphic information contained upon a page of a document by copying the information upon a microimage, or light transmissive plate which is greatly reduced in size from the page. It is also well known to position the microimages of a given document or related documents upon a single sheet of film, or microfiche, which has a standard size and a standard array of spaces for each microimage. A common microfiche format is that of the National Micrographic Association (NMA), which prescribes microfiche of six inches by four inches, each sheet provided with a 14.times.7 matrix array of spaces for microimages, and some or all the spaces being occupied by microimages.
To transmit information contained upon microfiche to a remote location in a manner which avoids physical transfer of the microfiche, various systems have been developed for successively scanning sheets of microfiche containing the required information. The output of such a system is a series of electrical signals in which the information is encoded and which is readily communicable to the remote location. However, such scanning systems as are presently available generally are unable to simultaneously scan more than one microimage at a given time or to simultaneously scan all points across the entire width of the microimage. Rather, most presently available systems must sweep a light source across the width of a microimage, sensing light intensity at different points or pixels (picture elements) at different times during the sweep with a light sensitive device.
In addition, a microfiche of the above type, having a given number of microfiche spaces, may contain fewer microimages than the number of spaces. If a scanning apparatus was not provided with a means for sensing unoccupied or blank spaces, all parts of a blank space would be scanned and converted to electrical signals. Because such signals would represent no graphic information, their transmission to a remote location is unnecessary. Their elimination would result in lower cost for a transmission link to the location.